At the Peng Mok Harbor in Jindo, about 20 kilometers (12 miles) from the site of the accident, family members spend the hours staring at the water.

They have camped out here since Wednesday. Mothers and grandmothers huddle together, crying and comforting each other.

Chang Min, whose son is a second-grader, said he was furious that search officials are using the word "investigation" and not the word "rescue."

"If the government cares for the people, our family, our children, please rescue our families and our children," he said.

He, like many others, are angry at the pace of the process.

Rescue officials are at the mercy of the elements. It's drizzling, making for poor visibility. The water currents are powerful, making for dangerous operations.

Three divers who took it upon themselves to go look for the missing were momentarily swept away by the tide Thursday, CNN affiliate YTN reported. A fishing boat eventually picked them up.

On Thursday afternoon, rescue crews were trying to get a crane out to stabilize the ship.

Hope for survival

The hope for survivors largely hinges on whether trapped passengers are in isolated pockets of air on the ship.

"From the images that I've seen, there's clearly some areas of the hull that are above the water, that are not flooded," Mike Dean, the U.S. Navy deputy director for salvage and diving, told "CNN Tonight."

"So absolutely, there could be areas in there where there is breathable air, but the trouble right now is the temperature and getting people to them."

Most of the bedrooms of the 353 passengers were on the fourth level of the five-floor boat.

That announcement, some witnesses worried, may have cost some passengers on the ferry their lives.

"We were told to stay where you are, so we kept staying," survivor Hyun Hung Chang told YTN. "But later on, the water level came up. So we were beside ourselves. Kids were screaming out of terror, shouting for help."

"Kids were forced to stay put," another survivor told YTN. "So only some of those who moved survived."

Waking up hearing that South Korea's ferry sank makes my stomach drop. Lets us take a moment & pray for their safety pic.twitter.com/e39Ygrh5iF

Many of the passengers aboard the ship were students of Ansan Danwon High School on a four-day trip to the resort island of Jeju.

At the school in the suburb of Seoul, parents sat on mats, clutching their cell phones for calls or texts from their children.

Local media reported on several text messages they said were from passengers. In one, a passenger describes women screaming in the darkness. In another, a father learns his child is trapped. In a third, a son, fearing death, tells his mother he loves her.

CNN could not independently confirm the authenticity of the messages or when they were sent. It's also unclear what happened to the people who sent them.

The panicked messages were reason enough for some parents to believe more survivors will be found.

On one wall of the school, officials have posted a list of names. Once a confirmation of a rescue came, they circled that name. On Wednesday, soon after the ship sank, several names were circled in rapid succession.

So many, however, remain untouched.

At one point Wednesday, the school announced that all students had been rescued but soon backtracked, to the parents' wrath.

Even though the school was closed Thursday, students and teachers arrived to seek comfort in numbers.

"Please be alive," said messages written in classroom chalkboards. "Please come back."

On Thursday, several parents took a boat to try to go the accident site. The boat turned back after several of them became so distraught that they fainted.

Explanations elusive

The five-story passenger ferry, Sewol, was carrying 475 passengers -- most of them students -- as it left from the port city of Incheon, just west of Seoul, for a trip to Jeju, the resort island considered the Hawaii of Korea.

Foggy weather had delayed the departure by about two hours.

Just before 9 a.m. Wednesday (8 p.m. Tuesday ET), about 12 miles from the island of Jindo, the ship ran into trouble.

Passenger Kim Sung-Mook told YTN he was eating breakfast in the ship's main hall when he felt the ferry begin to tilt.

Someone made the announcement telling passengers to stay in place. Then, Kim said, he heard a loud bang.

Student Lim Hyung Min, who was rescued, told YTN he heard the bang before the ship began to list.

"The students were falling over and crashing into things and bleeding," Lim said.

Ret. Capt. Jim Staples told "AC 360" that the ship's captain may have increased speed to remain on schedule.

Mary Schiavo, former inspector general for the Department of Transportation, thinks the ship could have hit something.

The ship's operator, Chonghaejin Marine Co., had no explanation -- only apologies.